From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B7127C433EF for ; Tue, 4 Jan 2022 15:15:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234795AbiADPPd (ORCPT ); Tue, 4 Jan 2022 10:15:33 -0500 Received: from foss.arm.com ([217.140.110.172]:60696 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229934AbiADPP3 (ORCPT ); Tue, 4 Jan 2022 10:15:29 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5A89413A1; Tue, 4 Jan 2022 07:15:29 -0800 (PST) Received: from [192.168.99.12] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 25AA03F774; Tue, 4 Jan 2022 07:15:28 -0800 (PST) Message-ID: <03a8fcbe-4f35-757a-b3f6-b3fdaa22966c@foss.arm.com> Date: Tue, 4 Jan 2022 15:15:27 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH 04/12] perf test: Add beginning of test infra + test to exercise coresight Content-Language: en-US To: Arnaldo Carvalho de Melo , Leo Yan Cc: linux-kernel@vger.kernel.org, coresight@lists.linaro.org, suzuki.poulose@arm.com, mathieu.poirier@linaro.org, mike.leach@linaro.org, inux-perf-users@vger.kernel.org References: <20211215160403.69264-1-carsten.haitzler@foss.arm.com> <20211215160403.69264-4-carsten.haitzler@foss.arm.com> <20211221150349.GB41974@leoy-ThinkPad-X240s> From: Carsten Haitzler Organization: Arm Ltd. In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/21/21 20:40, Arnaldo Carvalho de Melo wrote: > Em Tue, Dec 21, 2021 at 11:03:49PM +0800, Leo Yan escreveu: >> Hi Carsten, >> >> On Wed, Dec 15, 2021 at 04:03:55PM +0000, carsten.haitzler@foss.arm.com wrote: >>> From: Carsten Haitzler >>> >>> This adds the initial test harness to run perf record and examine the >>> resuling output when coresight is enabled on arm64 and check the >>> resulting quality of the output as part of perf test. >>> >>> Signed-off-by: Carsten Haitzler >>> --- >>> MAINTAINERS | 3 + >>> tools/perf/Makefile.perf | 14 +- >>> .../tests/shell/coresight_asm_pure_loop.sh | 18 +++ >>> tools/perf/tests/shell/lib/coresight.sh | 130 ++++++++++++++++++ >>> tools/perf/tests/shell/tools/Makefile | 26 ++++ >>> .../perf/tests/shell/tools/coresight/Makefile | 27 ++++ >>> .../shell/tools/coresight/Makefile.miniconfig | 23 ++++ >>> .../tools/coresight/asm_pure_loop/Makefile | 30 ++++ >>> .../coresight/asm_pure_loop/asm_pure_loop.S | 28 ++++ >>> 9 files changed, 297 insertions(+), 2 deletions(-) >>> create mode 100755 tools/perf/tests/shell/coresight_asm_pure_loop.sh >>> create mode 100644 tools/perf/tests/shell/lib/coresight.sh >>> create mode 100644 tools/perf/tests/shell/tools/Makefile >>> create mode 100644 tools/perf/tests/shell/tools/coresight/Makefile >>> create mode 100644 tools/perf/tests/shell/tools/coresight/Makefile.miniconfig >>> create mode 100644 tools/perf/tests/shell/tools/coresight/asm_pure_loop/Makefile >>> create mode 100644 tools/perf/tests/shell/tools/coresight/asm_pure_loop/asm_pure_loop.S >> >> The folder naming is okay for me, but it is cyclic with the format: >> "tools/.../tools/". So I am wandering if below two pathes are better? >> >> tools/perf/tests/shell/prog/coresight/ >> or >> tools/perf/tests/shell/coresight/ > > The later, its descriptive enough, I think, and the shortest variant so > far. Sure - no problem. I can change that. Once no one has any more comments and a few of the pending thnigs I've marked to resolve are solved, I'll submit a new patch set. > - Arnaldo > >> I'd like to leave this question for Arnaldo / Jiri for the folder >> layout. >> >>> diff --git a/MAINTAINERS b/MAINTAINERS >>> index 13f9a84a617e..d46e8469c467 100644 >>> --- a/MAINTAINERS >>> +++ b/MAINTAINERS >>> @@ -1894,6 +1894,9 @@ F: tools/perf/arch/arm/util/auxtrace.c >>> F: tools/perf/arch/arm/util/cs-etm.c >>> F: tools/perf/arch/arm/util/cs-etm.h >>> F: tools/perf/arch/arm/util/pmu.c >>> +F: tools/perf/tests/shell/coresight_* >>> +F: tools/perf/tests/shell/tools/Makefile >>> +F: tools/perf/tests/shell/tools/coresight/* >>> F: tools/perf/util/cs-etm-decoder/* >>> F: tools/perf/util/cs-etm.* >>> >>> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf >>> index 80522bcfafe0..26467a2c71f4 100644 >>> --- a/tools/perf/Makefile.perf >>> +++ b/tools/perf/Makefile.perf >>> @@ -630,7 +630,15 @@ sync_file_range_tbls := $(srctree)/tools/perf/trace/beauty/sync_file_range.sh >>> $(sync_file_range_arrays): $(linux_uapi_dir)/fs.h $(sync_file_range_tbls) >>> $(Q)$(SHELL) '$(sync_file_range_tbls)' $(linux_uapi_dir) > $@ >>> >>> -all: shell_compatibility_test $(ALL_PROGRAMS) $(LANG_BINDINGS) $(OTHER_PROGRAMS) >>> +TESTS_TOOLS_DIR := $(srctree)/tools/perf/tests/shell/tools >>> + >>> +tests-tools-targets: FORCE >>> + $(Q)$(MAKE) -C $(TESTS_TOOLS_DIR) >>> + >>> +tests-tools-targets-clean: >>> + $(Q)$(MAKE) -C $(TESTS_TOOLS_DIR) clean >>> + >>> +all: shell_compatibility_test $(ALL_PROGRAMS) $(LANG_BINDINGS) $(OTHER_PROGRAMS) tests-tools-targets >>> >>> # Create python binding output directory if not already present >>> _dummy := $(shell [ -d '$(OUTPUT)python' ] || mkdir -p '$(OUTPUT)python') >>> @@ -1020,6 +1028,7 @@ install-tests: all install-gtk >>> $(INSTALL) tests/shell/*.sh '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell'; \ >>> $(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell/lib'; \ >>> $(INSTALL) tests/shell/lib/*.sh '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell/lib' >>> + $(Q)$(MAKE) -C tests/shell/tools install-tests >>> >>> install-bin: install-tools install-tests install-traceevent-plugins >>> >>> @@ -1088,7 +1097,7 @@ endif # BUILD_BPF_SKEL >>> bpf-skel-clean: >>> $(call QUIET_CLEAN, bpf-skel) $(RM) -r $(SKEL_TMP_OUT) $(SKELETONS) >>> >>> -clean:: $(LIBTRACEEVENT)-clean $(LIBAPI)-clean $(LIBBPF)-clean $(LIBSUBCMD)-clean $(LIBPERF)-clean fixdep-clean python-clean bpf-skel-clean >>> +clean:: $(LIBTRACEEVENT)-clean $(LIBAPI)-clean $(LIBBPF)-clean $(LIBSUBCMD)-clean $(LIBPERF)-clean fixdep-clean python-clean bpf-skel-clean tests-tools-targets-clean >>> $(call QUIET_CLEAN, core-objs) $(RM) $(LIBPERF_A) $(OUTPUT)perf-archive $(OUTPUT)perf-with-kcore $(OUTPUT)perf-iostat $(LANG_BINDINGS) >>> $(Q)find $(if $(OUTPUT),$(OUTPUT),.) -name '*.o' -delete -o -name '\.*.cmd' -delete -o -name '\.*.d' -delete >>> $(Q)$(RM) $(OUTPUT).config-detected >>> @@ -1155,5 +1164,6 @@ FORCE: >>> .PHONY: shell_compatibility_test please_set_SHELL_PATH_to_a_more_modern_shell >>> .PHONY: $(GIT-HEAD-PHONY) TAGS tags cscope FORCE prepare >>> .PHONY: libtraceevent_plugins archheaders >>> +.PHONY: $(TESTS_TOOLS_TARGETS) >>> >>> endif # force_fixdep >>> diff --git a/tools/perf/tests/shell/coresight_asm_pure_loop.sh b/tools/perf/tests/shell/coresight_asm_pure_loop.sh >>> new file mode 100755 >>> index 000000000000..542d4a37e349 >>> --- /dev/null >>> +++ b/tools/perf/tests/shell/coresight_asm_pure_loop.sh >>> @@ -0,0 +1,18 @@ >>> +#!/bin/sh -e >>> +# Coresight / ASM Pure Loop >>> + >>> +# SPDX-License-Identifier: GPL-2.0 >>> +# Carsten Haitzler , 2021 >>> + >>> +TEST="asm_pure_loop" >>> +. $(dirname $0)/lib/coresight.sh >>> +ARGS="" >>> +DATV="out" >>> +DATA="$DATD/perf-$TEST-$DATV.data" >>> + >>> +perf record $PERFRECOPT -o "$DATA" "$BIN" $ARGS >> >> Is $ARGS redundant and can be removed? >> >>> +perf_dump_aux_verify "$DATA" 2601 334 334 >> >> These three magic numbers "2601 334 334" would be hard to understand. >> One way is the code can dynamically calculate these values based on the >> loop times (the loop is is predefined in asm_pure_loop.S), or it's >> good to give explanation in comments for these values. >> >>> + >>> +err=$? >>> +exit $err >>> diff --git a/tools/perf/tests/shell/lib/coresight.sh b/tools/perf/tests/shell/lib/coresight.sh >>> new file mode 100644 >>> index 000000000000..cd6c1283e6f5 >>> --- /dev/null >>> +++ b/tools/perf/tests/shell/lib/coresight.sh >>> @@ -0,0 +1,130 @@ >>> +# SPDX-License-Identifier: GPL-2.0 >>> +# Carsten Haitzler , 2021 >>> + >>> +# This is sourced from a driver script so no need for #!/bin... etc. at the >>> +# top - the assumption below is that it runs as part of sourcing after the >>> +# test sets up some basic env vars to say what it is. >>> + >>> +# perf record options for the perf tests to use >>> +PERFRECMEM="-m ,128M" >> >> We must use 128Mb for the AUX trace buffer? The big buffer size is >> not friendly for embedded system. >> >>> +PERFRECOPT="$PERFRECMEM -e cs_etm//u" >>> + >>> +# These tests need to be run as root or coresight won't allow large buffers >>> +# and will not collect proper data >>> +UID=`id -u` >>> +if test "$UID" -ne 0; then >>> + echo "Not running as root... skip" >>> + exit 2 >>> +fi >>> + >>> +TOOLS=$(dirname $0)/tools >>> +DIR="$TOOLS/coresight/$TEST" >>> +BIN="$DIR/$TEST" >>> +# If the test tool/binary does not exist and is executable then skip the test >>> +if ! test -x "$BIN"; then exit 2; fi >>> +DATD="." >> >> It's blur to set DATD and STATD to ".". If the user doesn't specify >> the envs, it's not clear it will point to which folder. >> >>> +# If the data dir env is set then make the data dir use that instead of ./ >>> +if test -n "$PERF_TEST_CORESIGHT_DATADIR"; then >>> + DATD="$PERF_TEST_CORESIGHT_DATADIR"; >>> +fi >>> +# If the stat dir env is set then make the data dir use that instead of ./ >>> +STATD="." >>> +if test -n "$PERF_TEST_CORESIGHT_STATDIR"; then >>> + STATD="$PERF_TEST_CORESIGHT_STATDIR"; >>> +fi >>> + >>> +# Called if the test fails - error code 2 >>> +err() { >>> + echo "$1" >>> + exit 1 >>> +} >>> + >>> +# Check that some statistics from our perf >>> +check_val_min() { >>> + STATF="$4" >>> + if test "$2" -lt "$3"; then >>> + echo ", FAILED" >> "$STATF" >>> + err "Sanity check number of $1 is too low ($2 < $3)" >>> + fi >>> +} >>> + >>> +perf_dump_aux_verify() { >>> + # Some basic checking that the AUX chunk contains some sensible data >>> + # to see that we are recording something and at least a minimum >>> + # amount of it. We should almost always see F3 atoms in just about >>> + # anything but certainly we will see some trace info and async atom >>> + # chunks. >>> + DUMP="$DATD/perf-tmp-aux-dump.txt" >>> + perf report --stdio --dump -i "$1" | \ >>> + grep -o -e I_ATOM_F3 -e I_ASYNC -e I_TRACE_INFO > "$DUMP" >>> + # Simply count how many of these atoms we find to see that we are >>> + # producing a reasonable amount of data - exact checks are not sane >>> + # as this is a lossy process where we may lose some blocks and the >>> + # compiler may produce different code depending on the compiler and >>> + # optimization options, so this is rough just to see if we're >>> + # either missing almost all the data or all of it >>> + ATOM_F3_NUM=`grep I_ATOM_F3 "$DUMP" | wc -l` >>> + ATOM_ASYNC_NUM=`grep I_ASYNC "$DUMP" | wc -l` >>> + ATOM_TRACE_INFO_NUM=`grep I_TRACE_INFO "$DUMP" | wc -l` >>> + rm -f "$DUMP" >>> + >>> + # Arguments provide minimums for a pass >>> + CHECK_F3_MIN="$2" >>> + CHECK_ASYNC_MIN="$3" >>> + CHECK_TRACE_INFO_MIN="$4" >>> + >>> + # Write out statistics, so over time you can track results to see if >>> + # there is a pattern - for example we have less "noisy" results that >>> + # produce more consistent amounts of data each run, to see if over >>> + # time any techinques to minimize data loss are having an effect or >>> + # not >>> + STATF="$STATD/stats-$TEST-$DATV.csv" >>> + if ! test -f "$STATF"; then >>> + echo "ATOM F3 Count, Minimum, ATOM ASYNC Count, Minimum, TRACE INFO Count, Minimum" > "$STATF" >>> + fi >>> + echo -n "$ATOM_F3_NUM, $CHECK_F3_MIN, $ATOM_ASYNC_NUM, $CHECK_ASYNC_MIN, $ATOM_TRACE_INFO_NUM, $CHECK_TRACE_INFO_MIN" >> "$STATF" >>> + >>> + # Actually check to see if we passed or failed. >>> + check_val_min "ATOM_F3" "$ATOM_F3_NUM" "$CHECK_F3_MIN" "$STATF" >>> + check_val_min "ASYNC" "$ATOM_ASYNC_NUM" "$CHECK_ASYNC_MIN" "$STATF" >>> + check_val_min "TRACE_INFO" "$ATOM_TRACE_INFO_NUM" "$CHECK_TRACE_INFO_MIN" "$STATF" >>> + echo ", Ok" >> "$STATF" >>> +} >>> + >>> +perf_dump_aux_tid_verify() { >> >> This function is not used in the test contained in this patch. >> >>> + # Specifically crafted test will produce a list of Tread ID's to >>> + # stdout that need to be checked to see that they have had trace >>> + # info collected in AUX blocks in the perf data. This will go >>> + # through all the TID's that are listed as CID=0xabcdef and see >>> + # that all the Thread IDs the test tool reports are in the perf >>> + # data AUX chunks >>> + >>> + # The TID test tools will print a TID per stdout line that are being >>> + # tested >>> + TIDS=`cat "$2"` >>> + # Scan the perf report to find the TIDs that are actually CID in hex >>> + # and build a list of the ones found >>> + FOUND_TIDS=`perf report --stdio --dump -i "$1" | \ >>> + grep -o "CID=0x[0-9a-z]\+" | sed 's/CID=//g' | \ >>> + uniq | sort | uniq` >>> + >>> + # Iterate over the list of TIDs that the test says it has and find >>> + # them in the TIDs found in the perf report >>> + MISSING="" >>> + for TID2 in $TIDS; do >>> + FOUND="" >>> + for TIDHEX in $FOUND_TIDS; do >>> + TID=`printf "%i" $TIDHEX` >>> + if test "$TID" -eq "$TID2"; then >>> + FOUND="y" >>> + break >>> + fi >>> + done >>> + if test -z "$FOUND"; then >>> + MISSING="$MISSING $TID" >>> + fi >>> + done >>> + if test -n "$MISSING"; then >>> + err "Thread IDs $MISSING not found in perf AUX data" >>> + fi >>> +} >>> diff --git a/tools/perf/tests/shell/tools/Makefile b/tools/perf/tests/shell/tools/Makefile >>> new file mode 100644 >>> index 000000000000..c7ada20922fd >>> --- /dev/null >>> +++ b/tools/perf/tests/shell/tools/Makefile >>> @@ -0,0 +1,26 @@ >>> +# SPDX-License-Identifier: GPL-2.0-only >>> +# Carsten Haitzler , 2021 >>> +include ../../../../../tools/scripts/Makefile.include >>> +include ../../../../../tools/scripts/Makefile.arch >>> +include ../../../../../tools/scripts/utilities.mak >> >> To be honest, I don't understand well for perf's build and config >> system. Seems to me, a good example for building program is jevents. >> >> Please take a look for the code: >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/Makefile.perf#n667 >> >> If follow the same method with jevents for building test programs, >> I can see one benefit is we don't need to create a Makefile, on the >> other hand, we can reuse the perf's build system and simply create a >> Build file under the folder tools/perf/tests/shell/.../coresight/. >> >>> + >>> +SUBDIRS = \ >>> + coresight >>> + >>> +all: $(SUBDIRS) >>> +$(SUBDIRS): >>> + $(Q)$(MAKE) -C $@ >>> + >>> +INSTALLDIRS = $(SUBDIRS:%=install-%) >>> + >>> +install-tests: all $(INSTALLDIRS) >>> +$(INSTALLDIRS): >>> + $(Q)$(MAKE) -C $(@:install-%=%) install-tests >>> + >>> +CLEANDIRS = $(SUBDIRS:%=clean-%) >>> + >>> +clean: $(CLEANDIRS) >>> +$(CLEANDIRS): >>> + $(Q)$(MAKE) -C $(@:clean-%=%) O=$(OUTPUT) clean >/dev/null >>> + >>> +.PHONY: all clean install-tests $(SUBDIRS) $(CLEANDIRS) $(INSTALLDIRS) >>> diff --git a/tools/perf/tests/shell/tools/coresight/Makefile b/tools/perf/tests/shell/tools/coresight/Makefile >>> new file mode 100644 >>> index 000000000000..723006ea827c >>> --- /dev/null >>> +++ b/tools/perf/tests/shell/tools/coresight/Makefile >>> @@ -0,0 +1,27 @@ >>> +# SPDX-License-Identifier: GPL-2.0-only >>> +# Carsten Haitzler , 2021 >>> +include ../../../../../../tools/scripts/Makefile.include >>> +include ../../../../../../tools/scripts/Makefile.arch >>> +include ../../../../../../tools/scripts/utilities.mak >>> + >>> +SUBDIRS = \ >>> + asm_pure_loop >>> + >>> +all: $(SUBDIRS) >>> +$(SUBDIRS): >>> + $(Q)$(MAKE) -C $@ >>> + >>> +INSTALLDIRS = $(SUBDIRS:%=install-%) >>> + >>> +install-tests: $(INSTALLDIRS) >>> +$(INSTALLDIRS): >>> + $(Q)$(MAKE) -C $(@:install-%=%) install-tests >>> + >>> +CLEANDIRS = $(SUBDIRS:%=clean-%) >>> + >>> +clean: $(CLEANDIRS) >>> +$(CLEANDIRS): >>> + $(Q)$(MAKE) -C $(@:clean-%=%) clean >/dev/null >>> + >>> +.PHONY: all clean $(SUBDIRS) $(CLEANDIRS) $(INSTALLDIRS) >>> + >>> diff --git a/tools/perf/tests/shell/tools/coresight/Makefile.miniconfig b/tools/perf/tests/shell/tools/coresight/Makefile.miniconfig >>> new file mode 100644 >>> index 000000000000..cedd26c6a0eb >>> --- /dev/null >>> +++ b/tools/perf/tests/shell/tools/coresight/Makefile.miniconfig >>> @@ -0,0 +1,23 @@ >>> +# SPDX-License-Identifier: GPL-2.0-only >>> +# Carsten Haitzler , 2021 >>> + >>> +ifndef DESTDIR >>> +prefix ?= $(HOME) >>> +endif >>> + >>> +DESTDIR_SQ = $(subst ','\'',$(DESTDIR)) >>> +perfexecdir = libexec/perf-core >>> +perfexec_instdir = $(perfexecdir) >>> + >>> +ifneq ($(filter /%,$(firstword $(perfexecdir))),) >>> +perfexec_instdir = $(perfexecdir) >>> +else >>> +perfexec_instdir = $(prefix)/$(perfexecdir) >>> +endif >>> + >>> +perfexec_instdir_SQ = $(subst ','\'',$(perfexec_instdir)) >>> +INSTALL = install >>> + >>> +include ../../../../../../scripts/Makefile.include >>> +include ../../../../../../scripts/Makefile.arch >>> +include ../../../../../../scripts/utilities.mak >> >> As suggested above, if we refer the building method of jevent, I think >> this Makefile.miniconfig is not needed anymore. >> >>> diff --git a/tools/perf/tests/shell/tools/coresight/asm_pure_loop/Makefile b/tools/perf/tests/shell/tools/coresight/asm_pure_loop/Makefile >>> new file mode 100644 >>> index 000000000000..10c5a60cb71c >>> --- /dev/null >>> +++ b/tools/perf/tests/shell/tools/coresight/asm_pure_loop/Makefile >>> @@ -0,0 +1,30 @@ >>> +# SPDX-License-Identifier: GPL-2.0 >>> +# Carsten Haitzler , 2021 >>> + >>> +include ../Makefile.miniconfig >>> + >>> +BIN=asm_pure_loop >>> +LIB= >>> + >>> +all: $(BIN) >>> + >>> +$(BIN): $(BIN).S >>> +ifdef CORESIGHT >>> +ifeq ($(ARCH),arm64) >>> + $(Q)$(CC) $(BIN).S -nostdlib -static -o $(BIN) $(LIB) >>> +endif >>> +endif >>> + >>> +install-tests: all >>> +ifdef CORESIGHT >>> +ifeq ($(ARCH),arm64) >>> + $(call QUIET_INSTALL, tests) \ >>> + $(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell/tools/$(BIN)'; \ >>> + $(INSTALL) $(BIN) '$(DESTDIR_SQ)$(perfexec_instdir_SQ)/tests/shell/tools/$(BIN)/$(BIN)' >>> +endif >>> +endif >>> + >>> +clean: >>> + $(Q)$(RM) -f $(BIN) >>> + >>> +.PHONY: all clean install-tests >>> diff --git a/tools/perf/tests/shell/tools/coresight/asm_pure_loop/asm_pure_loop.S b/tools/perf/tests/shell/tools/coresight/asm_pure_loop/asm_pure_loop.S >>> new file mode 100644 >>> index 000000000000..262876451021 >>> --- /dev/null >>> +++ b/tools/perf/tests/shell/tools/coresight/asm_pure_loop/asm_pure_loop.S >>> @@ -0,0 +1,28 @@ >>> +/* SPDX-License-Identifier: GPL-2.0 */ >>> +/* Tamas Zsoldos , 2021 */ >>> + >>> +.globl _start >>> +_start: >>> + mov x0, 0x000fffff >>> + mov x1, xzr >>> +loop: >>> + nop >>> + nop >>> + cbnz x1, noskip >>> + nop >>> + nop >>> + adrp x2, skip >>> + add x2, x2, :lo12:skip >>> + br x2 >>> + nop >>> + nop >>> +noskip: >>> + nop >>> + nop >>> +skip: >>> + sub x0, x0, 1 >>> + cbnz x0, loop >>> + >>> + mov x0, #0 >>> + mov x8, #93 // __NR_exit syscall >>> + svc #0 >> >> I verified this code on Arm64 machine and it works! >> >> I am a bit worry about the code for using the hard code number for >> system call. Another option is to use the inline assembly >> in C code, I think you have considered for this approach, this might >> introduce noise for extra branch instructions during the testing, >> but it can allow us to program standard C program (and don't worry >> about the program exiting). >> >> If you think using assembly code is better than inline assembly, it >> would be fine for me. Eventually, the system call number is very >> seldomly to be changed. >> >> Thanks, >> Leo >